There is a switching power supply apparatus such as a direct current to direct current converter (DC-DC converter) that converts a high voltage direct current into an alternating current by using a switching operation and then converts the alternating current into a low voltage direct current. A magnetic device such as a choke coil or a transformer is used in the switching power supply apparatus.
For example, JP-A-7-38262, JP-A-7-86755, JP-A-2010-109309, JP-A-2011-29313, JP-A-2012-156461 and JP-A-2008-177516 disclose a coil-integrated printed circuit board on which a coil pattern made of an electric conductor is formed as a coil winding wire, and a magnetic device provided with the board.
The coil pattern is made of a metallic foil having electric conductivity, for example, a copper foil. Similarly, each of the electric conductors such as other wiring patterns, a pad or the like of the board is made of a metallic foil. The coil pattern includes an outer layer that is exposed to the outside of the board, and an inner layer that is not exposed to the outside.
In JP-A-7-38262, JP-A-7-86755 and JP-A-2012-156461, a core made of a magnetic material passes through the board. The coil pattern is formed on predetermined layers of the board so as to be wound around the core.
In JP-A-2011-29313 and JP-A-2012-156461, a thick electric conductor board is used in which the electric conductor of the coil pattern or the like has a thickness greater than that of a typical electric conductor provided on the board so as to allow a large current to flow therethrough.
In JP-A-7-38262, JP-A-7-86755 and JP-A-2010-109309, the respective coil patterns of different layers are connected to each other via a through hole or a copper pin.
In JP-A-7-38262, JP-A-7-86755, JP-A-2010-109309 and JP-A-2011-29313, other electronic components are mounted in a region that is separate from the coil pattern on a top surface layer of the board, and other electrical circuits are formed.
In JP-A-2008-177516, the board includes a pair of insulating layers and a magnetic layer that is interposed between the insulating layers. The coil pattern is formed on the magnetic layer.